Monitoring intracranial pressure (ICP) in real time in intensive care units has become an established standard of care in guiding physicians in the management of severe head injury. Treatment of head trauma increases pressure on the brain requiring monitoring intracranial pressure. This is particularly true in complicated cases of hydrocephalus as a post-craniotomy adjunct to detect brain swelling and in selected instances of brain infection and stroke. As brain swelling worsens due to the disease process, baseline pressure and waveform changes signal the need to aggressively attempt to reverse the course of the swelling with medications and pulmonary ventilation changes.
Intracranial pressure monitoring is normally performed by inserting a shunt through a hole in the cranium. A ventriculostomy catheter connected to an external pressure transducer is then introduced via the shunt into the brain substance. The shunt may also be used to drain excess fluid from the brain substance. An external pressure transducer provides accurate pressure measurements since a reliable baseline may be established. However, an external pressure transducer requires invasive procedures, risking a patient's health.
More recently, a miniaturized fiberoptic or strain gauge pressure transducer is inserted into the brain substance. The miniaturized transducer greatly reduces the invasiveness of the insertion procedure, but no practical method exists to establish a baseline measurement. This creates accuracy problems since many factors over the course of treatment may shift baseline measurements. Additionally, the ICP sensor and data from it alone do not allow a direct measurement of how edematous or congested the specific region of the brain is. Furthermore, swelling provides a widely ranging pressure change related to age and causes of the swelling. Finally, the ICP sensor alone does not provide a measurement of real time brain stiffness or compliance, a helpful indicator of imminent deterioration risk.
Static measurement may be achieved by magnetic resonance imaging (“MRI”), but this does not provide real time data. Real time information would greatly facilitate the detection of true shunt failure in the management of hydrocephalus. However, since real time measurement cannot be done with internal sensors, shunt failure must be inferred from late presenting clinical deterioration and anatomical changes as seen in imaging studies of the MRI. Additionally, the transport of a critically ill patient to an MRI facility is hazardous.
There is therefore a need for an instrument which may be inserted through a single aperture in the skull for simultaneous and continuous monitoring of both intracranial pressure and cerebral water content. There is another need for an instrument which may continuously measure pulsatile changes, altering apparent water content relating to beat-to-beat tissue perfusion due to cardiac output of blood to the brain. There is a further need for an instrument which provides the continuous measurement of tissue congestion related to venous back pressure from mechanical ventilation. There is another need for an instrument which derives the percent water content of the brain for comparison against normal values. There is yet another need for a system to monitor the more gradual baseline changes in wetness or brain edema of intracellular or extracellular origin related to the disease process. There is another need for an instrument which can simultaneously display the intracranial pressure (ICP) waveform and the pulsatile perfusional or momentary congestion changes of the brain. There is still another need for an apparatus and method for comparing the differences in lagtime between the ICP and perfusional waveforms, from which a realtime measurement of brain stiffness or compliance is derived.